This project describes a code practice oscillator that I used way back when. You might say that this is behind the times, but when I get bored of SSB, I dust off the old straight key and have a few contacts on 7.040 MHz just to keep my code ear going. It is a more challenging than SSB, and I find that I get a sense of satisfaction after a contact.

The article also describes some basic electronic theory such as oscillators, transistor switches and audio amplifiers. So if you want to learn code, here is a neat little project.